The Leachability of Calcium Aluminate Phases in Slags for the Extraction of Alumina

Abstract

Alumina is used primarily as feedstock for aluminum production. It occurs naturally in bauxite and clay and other minerals, and can be concentrated in industrial by-products such as coal gangue, fly ash, blast furnace slag, etc. The hydrometallurgical treatment of bauxite to recover alumina has been widely adopted industrially since the Bayer process was first employed commercially. However, the sustainability of alumina production by this means is less than ideal, due to the high production rate of poorly utilized and highly alkaline by-product that the process yields; bauxite residue or red mud. On the other hand, digestion of alumina-containing slags produced by reduction of bauxite results in no red mud production. In this work, the leachability of binary phases of CaO and Al2O3 in slags is studied under given conditions of temperature and time. Advanced characterization techniques are used to study the chemical composition, phases and microstructure of the slags and the digestion products. It is apparent that the leachability of a phase affects that of other phases. A less leachable phase could hinder the leachability of a more leachable phase. The experimental data shows that the leaching rate of slag from highest to the lowest is CaO.Al2O3, 3CaO.Al2O3, and CaO.2Al2O3 respectively.